Experimental investigation of the dynamics of partially premixed hydrogen flames in a lean direct injection (LDI) combustor

Lean hydrogen combustion is becoming increasingly popular for energy systems targeting decarbonisation using hydrogen. In this work, the characteristics of a partially premixed flame in a hydrogen lean direct injection (LDI) combustor were investigated. A jet-in-crossflow configuration was used in this combustor, with the hydrogen injected inwards through two diametrically opposite holes positioned on the circumference of a circular air channel. Heat release measurements were obtained with OH* chemiluminescence using, (i) photomultiplier tube (PMT), and (ii) intensified CMOS camera, while pressure measurements were conducted with high-sensitivity dynamic pressure transducers. Effects of bulk velocity and global equivalence ratio ( ϕ g l o b a l ) on flame behaviour and acoustic characteristics were studied. The flame images showed changes in the flame lift-off height and flame length as the ϕ g l o b a l was varied from rich to lean conditions. Mixture fraction results showed that an increase in both bulk velocity and ϕ g l o b a l improved mixing which was attributed to higher momentum flux ratio. High frequency pressure oscillations were observed at the leaner and richer ϕ g l o b a l conditions for 40 m/s and only at leaner conditions for 120 m/s. The heat release oscillations were observed to be coupled to the pressure oscillations for the higher frequency modes of the combustor at 40 m/s and 120 m/s. For both velocities, the largest amplitude of oscillations occurred at the ϕ g l o b a l conditions with the lowest average flame length. • Variation in the flame root positions, F R related to efficiency of fuel–air mixing. • Increasing the bulk velocity diminishes its effect on the flame length. • High frequency oscillations occurred at leaner and richer ϕ g l o b a l for 40 m/s. • At 120 m/s, high frequency oscillations occurred at only leaner ϕ g l o b a l conditions.